I've been asked to kind of sum up what is known so far. I'm just going to spill these things out and limit my own speculation:
So, back earlier in the game, Grok and John are the only two who failed a fort save from some kind of mysterious effect.
The false Grok that ran off and killed itself was apparently unrelated to the sores.
There are a number of weird and frightening things going on in this strange place, and the Phantasm Grok was one of the most powerful.
The book John recently read gives an indication as to the possible identity of the evil that infests and infects nearby creatures.
John believes that a recent ancestor (grandpa) has some kind of connection to current goings-on, and that the staff once belonged to him. The recently discovered piece of the staff supports this idea.
John also believes that grandpa hovers about and tries from time to time to guide him, like when the staff was first mysteriously revealed in the local church. John also only masturbates under his robe, 'cause he's pretty sure grandpa can't see there.
Scrag has a mysterious ring that came in a magical tube that spoke to him. The voice instructed him to slip it over one of his fangs and he did. The ring shrank to fit the tooth and is apparently bonded to it. He has no idea what the function of the ring might be. The voice in the tube told him he was to act as a protector to the lovely Rosalia.
Rosalia has a special background related to Scrag, but it's existence and details are not common knowledge at this time.
Grok and Roderic came to this town together, sent as a kind of joint inter-faith taskforce from their superiors to investigate and eliminate any unholy influences that may be plaguing the area.
Details in my memory are foggy, but I think Tuk is there because it seemed like a good idea at the time. He seems to have mercenary reasons, and is mostly unconcerned with the petty details.
John's staff is a mystery, and he has tried to use it before several times, but the only reaction he got so far was that it glows, and it's glow sometimes reveals things that mundane light does not.
I estimate lapsed time in game has been about 40-60 hours.
The holy or unholy (warlock) members of the party in particular have felt the presence of something terrible deep in the bowels of the mountain. Scrag also has some limited sensitivity to it, but it is less defined. In all cases, it is strong enough to be somewhat directional.

Fap! Fap! Fap!
Rosalia: Sshhh! I think I hear more kobolds running this way. Lemme bend over and put my ear to the ground...
FAPFAPFAPFAPFAPFAPFAPFAPFAP!
Tuk: You do that.
Rosalia: They're closing fast! Everybody ready!
Grok: What you doin', John?
John: Hold on... Almost there...
Roderic: I'll have no part in this.
Scrag: Mebe sumun should tell her.
Tuk: No. Not yet.
John: Rrrrr....ahhhhh...
Tuk: Ok. Now maybe he'll be able to concentrate better in our next battle.